package org.hccp.pdf;

import java.util.Vector;

/**
 *The cross-reference table contains information that permits random access to indirect
 *objects within the file, so that the entire file need not be read to locate any
 *particular object. The table contains a one-line entry for each indirect object,
 *specifying the location of that object within the body of the file.
 *<br>
 *<br>
 *The cross-reference table is the only part of a PDF file with a fixed format; this
 *permits entries in the table to be accessed randomly. The table comprises one or
 *more cross-reference sections. Initially, the entire table consists of a single section;
 *one additional section is added each time the file is updated.
 *<br>
 *<br>
 *Each cross-reference section begins with a line containing the keyword xref. Following
 *this line are one or more cross-reference subsections, which may appear in
 *any order. The subsection structure is useful for incremental updates, since it
 *allows a new cross-reference section to be added to the PDF file, containing
 *entries only for objects that have been added or deleted. For a file that has never
 *been updated, the cross-reference section contains only one subsection, whose
 *object numbering begins at 0.
 *
 * @see CrossReferenceTableEntryException
 * @see SubSection
 *
 **/


public class CrossReferenceTable implements DocumentObject {

    private static final String XREF = "xref";
    private Vector subSections;
    private Entry defaultEntry;
    private Body body;
    private Header header;
    
    
    public CrossReferenceTable() {
        subSections = new Vector();
        defaultEntry = new Entry();
    }
    
    public CrossReferenceTable(Header header, Body body)  {
        subSections = new Vector();
        defaultEntry = new Entry();
        this.body = body;
        this.header = header;
	
        SubSection subsection = new SubSection();
	
        defaultEntry.setObjectNumber("");
        defaultEntry.setGenNumber("65535"); // not sure if remember what this is doing. must check spec.
        defaultEntry.setIsFree(true);
        subsection.addEntry(defaultEntry);
        Vector vector = body.getBodyObjects();
        int i = header.getValue().getBytes().length;

        for(int j = 0; j < vector.size(); j++) {
            Entry entry = new Entry();
            defaultEntry.setObjectNumber("" + i);
            defaultEntry.setGenNumber("");
            subsection.addEntry(entry);
            i += ((DocumentObject)vector.elementAt(j)).getValue().getBytes().length;
        }

        subSections.add(subsection);
    }
    /**
     * Updates the cross-reference table in regards to document objects added to the PDF
     * document. Should be called prior to serialization, generation, or output of file.
     **/
    public void refresh() {
        SubSection subsection = (SubSection)subSections.elementAt(subSections.size() - 1);
        Vector vector = body.getBodyObjects();
        int i = header.getValue().getBytes().length;
        for(int j = 0; j < vector.size(); j++) {
            Entry entry = new Entry();
            entry.setObjectNumber("" + i);
            entry.setGenNumber("");
            subsection.addEntry(entry);
            i += ((DocumentObject)vector.elementAt(j)).getValue().getBytes().length;
        }

    }

    public void update(Header header, Body body) {
    	// no-op?
    }
    
    /**
     *
     * returns the specified subsection from this cross-reference table
     *
     * @param firstObject the object number of the start of the subsection to be returned.
     * @param objectCount the number of objects in the subsection to be returned.
     * @see SubSection
     * @return a {@link SubSection} object defined by the starting object number and number of objects in the subsection
     **/

    public SubSection getSubSection(int firstObject, int objectCount) {
        return new SubSection(firstObject, objectCount);
    }

    public String getValue()  {

        StringBuffer sb = new StringBuffer();
        sb.append(XREF);
        sb.append("\n");

        try {
            for(int i = 0; i < subSections.size(); i++) {
                sb.append(((SubSection)subSections.elementAt(i)).getValue());
			}
        } catch(CrossReferenceTableEntryException crtee) {
            sb.append(crtee.getMessage());
        }
        return sb.toString();
    }

}